1. Field of the Invention
This invention relates in general to well production systems, and in particular to a choke utilized with a subsea tree assembly.
2. Description of the Prior Art
In oil or gas well, a christmas tree will be mounted to a wellhead at the upper end of the well. The tree has outlets for the flow of production fluid. A choke will be mounted to the tree in a production passage. The choke restricts the fluid flow to a selected level to maintain adequate formation pressure.
Typically, a choke has a housing which has a bore. The bore is in communication with the tree production flow passage. The choke body fits inside the housing in a position where the production flow is required to flow through a portion of the choke body. The choke body is secured by a bonnet. Particularly for high pressure chokes, metal seals are used, with one of the seals being an inner seal. The inner seal, also referred to as a "bean" seal, surrounds the choke body and seals to the bore of the choke housing. A closure seal locates between the faces of the bonnet and choke housing. A recess or counterbore is located in the bore and joins the seal surface for the inner seal.
The choke body requires considerable force to insert and withdraw because of the metal inner seal. Hydraulically operated clamps are utilized in the case of high pressure subsea chokes for clamping the bonnet to the choke housing to force the inner seal from the counterbore area into the seal area. In high pressure chokes, it can be a difficult task to pull the choke body from the choke housing bore. Even though the clamps are released, the radially preloaded inner seal provides substantial frictional force, requiring a mechanical device to pull the choke body. This is particularly a problem in the case of a subsea well in deep water. An expensive piece of remotely operated equipment may be required to pull the choke.